1. Field of the Invention
The present invention relates, in general, to microwave ovens and, more particularly, to a microwave oven provided with a humidity sensor to sense humidity in the cooking cavity of the oven by sensing humidity of air exhausted from the cooking cavity.
2. Description of the Prior Art
A microwave oven is an electrically operated oven that uses a magnetron to generate high-frequency electromagnetic waves, which are waves having a fundamental frequency of 2450 MHz. The electromagnetic waves are radiated into a cooking cavity to repeatedly change the molecular arrangement of moisture laden in food, thus generating intermolecular frictional heat within the food which ultimately cooks the food.
In recent years, in order to meet a variety of requirements of consumers, a microwave oven with a humidity sensor has been proposed and used. In an operation of such a microwave oven, the humidity sensor determines the humidity of air inside the cooking cavity, and automatically controls the cooking process based upon this determination.
As shown in FIG. 1, a conventional microwave oven with a humidity sensor 6 comprises a body 1, the interior of which is partitioned into a cooking cavity 2 and a machine room 3. A door 4 is hinged to the body 1 so as to close the cooking cavity 2. The microwave oven also has a control panel 5, which is installed at a front wall of the body 1 and is provided with a variety of control buttons. The humidity sensor 6 is installed in the body 1 to sense the operational conditions of the food in the cooking cavity 2.
The cooking cavity 2 is opened at its front, and has a turntable-type cooking tray 2a rotatably mounted on the bottom of the cavity 2. An air inlet 7a is formed at a front portion of a sidewall 7 of the cooking cavity 2 so as to allow the cooking cavity 2 to communicate with the machine room 3. Air flows from the machine room 3 into the cooking cavity 2 through the air inlet 7a. An air outlet 8a is formed at a rear portion of an opposite sidewall 8 of the cooking cavity 2 so as to discharge air exhausted from the cooking cavity 2 to the atmosphere exterior to the body 1.
A magnetron 3a, a cooling fan 3b, an air guide duct 3c and other similar elements (not shown) are installed within the machine room 3. The magnetron 3a generates the high-frequency electromagnetic waves, while the cooling fan 3b sucks atmospheric air into the machine room 3 so as to cool the elements installed within the machine room 3. The air guide duct 3c guides the air inside the machine room 3 to the air inlet 7a. The cooling fan 3b is installed at a position between the magnetron 3a and a rear wall of the machine room 3. In order to allow atmospheric air to flow into the machine room 3 from exterior to the body 1, a predetermined area of the rear wall of the machine room 3 is perforated to form a plurality of air suction holes 3d. 
The humidity sensor 6 is installed on the sidewall 8 of the cooking cavity 2 at a position adjacent to the air outlet 8a. Thus, the humidity sensor 6 is placed in an air discharging passage leading from the cooking cavity 2 to the atmosphere exterior to the body 1. The humidity sensor 6 thus senses the humidity of the exhaust air discharged from the cooking cavity 2 through the air outlet 8a. This humidity sensor 6 is connected to a circuit board (not shown) installed in the control panel 5, and outputs a signal to the circuit board. When turning on the microwave oven containing food on the cooking tray 2a by manipulating the control panel 5, the high-frequency electromagnetic waves are radiated from the magnetron 3a into the cooking cavity 2 and the food is cooked.
During such an operation of the microwave oven the cooling fan 3b is rotated to form a suction force. The suction force sucks the atmospheric air into the machine room 3 through the air suction holes 3d and cools the elements installed in the room 3. The air is, thereafter, guided to the air inlet 7a by the air guide duct 3c and introduced into the cooking cavity 2 through the air inlet 7a. The air inside the cooking cavity 2 is exhausted along with the vapor generated from the food to the atmosphere through the air outlet 8a as shown by the arrows of FIG. 1. Therefore, it is possible to remove odor and vapor generated from food during the operation of the microwave oven.
When the exhaust air flows from the cooking cavity 2 to the atmosphere, it comes into contact with the humidity sensor 6. The humidity sensor 6 senses the humidity of the exhaust air, and outputs a signal to the circuit board of the control panel 5. The circuit board of the control panel 5 controls the operation of the magnetron 3a, the cooking tray 2a and the cooling fan 3b in response to the signal from the humidity sensor 6 to automatically cook the food on the tray 2a. 
However, the above conventional microwave oven is problematic since the humidity sensor 6 is installed at a position close to the air outlet 8a through which air is discharged from the cooking cavity 2 to the atmosphere exterior to the body 1. When the microwave oven sequentially performs several cooking processes, the air inside the cooking cavity 2 is excessively heated and discharged to the atmosphere through the air outlet 8a, which overheats the humidity sensor 6 and reduces the sensing performance of the sensor 6. In addition, moisture and contaminants, such as oil and smoke, generated from food during the cooking processes are deposited onto the surface of the humidity sensor 6 when they flow from the cooking cavity 2 to the atmosphere along with the exhaust air through the air outlet 8a. The moisture and contaminants deposited on the surface of the humidity sensor 6 are not easily removed from the humidity sensor 6, which further reduces the sensing performance of the humidity sensor 6.
In order to accomplish the above and other problems, an object of the present invention is to provide a microwave oven having a humidity sensor and an improved air outlet structure and humidity sensor mounting structure so as to prevent the humidity sensor from being overheated and/or contaminated by air exhausted from the cooking cavity.
An additional object of the present invention is to provide a microwave oven having a humidity sensor and an improved air outlet structure and humidity sensor mounting structure so as to prevent the humidity sensor from being overheated or contaminated by air exhausted from the cooking cavity, and to allow the humidity sensor to precisely sense the humidity of air inside the cooking cavity during a cooking process.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
In order to accomplish the above and other objects of the invention, a microwave oven includes a body including a cooking cavity and a machine room, a cooling fan installed in the machine room to suck atmospheric air through an air inlet into the cooking cavity while cooling a variety of elements installed in the machine room, an air outlet unit to discharge air from the cooking cavity, and a humidity sensor to sense operational conditions of the cooking cavity, wherein the air outlet unit includes a main-outlet formed at a sidewall of the cooking cavity to allow the cooking cavity to communicate with the atmospheric air exterior to the body, and a sub-outlet formed at an opposite sidewall of the cooking cavity to allow the cooking cavity to communicate with an air inlet side of the cooling fan, and the humidity sensor senses the humidity of air discharged from the cooking cavity through the sub-outlet.
According to an aspect of the invention, the machine room further includes an air guide to guide the air from the sub-outlet to the air inlet side of the cooling fan, and the humidity sensor is arranged on a rear surface of the air guide so as to be positioned adjacent to the sub-outlet.
According to another aspect of the invention, the machine room further includes an air suction hole at a rear wall to suck the atmospheric air into the machine room, and the humidity sensor is arranged adjacent to the air suction hole such that the moisture deposited on the humidity sensor is removed from the sensor by the atmospheric air sucked into the machine room through the air suction hole.
According to another embodiment of the present invention, a microwave oven includes a body including a cooking cavity and a machine room, a cooling fan installed in the machine room to suck atmospheric air into the cooking cavity through an air inlet while cooling a variety of elements installed in the machine room, an air outlet unit to discharge air from the cooking cavity, and a humidity sensor to sense operational conditions of food in the cooking cavity, wherein the air outlet unit includes a main-outlet formed at a sidewall of the cooking cavity to allow the cooking cavity to communicate with the atmospheric air exterior to the body, and a sub-outlet formed at an opposite sidewall of the cooking cavity to allow the cooking cavity to communicate with the air inlet side of the cooling fan, a ratio of the area of the sub-outlet to the total area of the main-outlet and the sub-outlet is roughly between 10 and 25%, and the humidity sensor senses the humidity of the air discharged from the cooking cavity through the sub-outlet.
According to another aspect of the invention, a ratio of the area of the main-outlet to the total area is roughly between 70 and 70%, and the ratio of the area of the sub-outlet to the total area is roughly between 20 and 25%.
According to a further embodiment of the present invention, a microwave oven includes a body including a cooking cavity and a machine room, a cooling fan installed in the machine room to suck atmospheric air exterior to the body into the cooking cavity and through an air inlet while cooling a variety of elements installed in the machine room, an air outlet unit to discharge air from the cooking cavity, and a humidity sensor to sense operational conditions of the cooking cavity, wherein the air outlet unit includes a main-outlet formed at a sidewall of the cooking cavity to allow the cooking cavity to communicate with the atmospheric air exterior to the body, and a sub-outlet formed at another sidewall of the cooking cavity to allow the cooking cavity to communicate with the air inlet side of the cooling fan, a sub-outlet piercing ratio of a total area of openings in the sub-outlet to a total area of the sub-outlet is 2% or more greater than an inlet piercing ratio of a total area of openings in the air inlet to a total area of the air inlet, and the humidity sensor senses the humidity of the air discharged from the cooking cavity through the sub-outlet.
According to a further aspect of the invention, the sub-outlet piercing ratio is 5% or more greater than the air inlet piercing ratio.